Field of the Invention
The present invention relates to a liquid ejection apparatus that performs printing on a printing medium by ejecting liquid. More specifically, the invention relates a circulation-type liquid ejection apparatus that circulates ink between a liquid storage container and a liquid ejection head, and the liquid ejection head mounted therein.
Description of the Related Art
There is a known circulation-type liquid ejection apparatus, which circulates ink between a liquid storage container and a liquid ejection head, represented by an inkjet printing apparatus. A line-type (page wide type) liquid ejection head in which a plurality of print element boards are disposed across a page width is mounted in a circulation-type liquid ejection apparatus corresponding to an example of the known circulation-type liquid ejection apparatus.
In such a liquid ejection apparatus, a pressure difference may be generated in a pressure applied to ink adjacent to each ejection opening in some cases. For example, a large amount of ink is supplied to an elongated liquid ejection head developed for commercial printing, and thus a pressure difference is easily generated around each ejection opening depending on printing duties. In addition, for example, in the circulation-type liquid ejection apparatus, a pressure variation generated when a circulation pump pulses may affect a pressure difference around each ejection opening in some cases. When printing is performed in a state in which an influence of the pressure difference is generated around each ejection opening, the volume of ink drops ejected from each ejection opening is non-uniform, which causes unevenness in density in a printed image to degrade an image quality.
Meanwhile, recently, a head has been proposed as a measure against bubbles in a passage or a measure against an influence on ejection due to thickening of ink around an ejection opening. The head has a form in which an ink supply path and an ink collection path are provided inside the liquid ejection head, and a pressure difference is generated between the supply path and the collection path, thereby generating an ink flow passing through an ejection opening. For example, US Patent Laid-Open No. 2013/0169710 proposes a liquid ejection apparatus that controls an ink supply path and an ink collection path such that the paths have different pressures using a plurality of pressure control mechanisms. The liquid ejection apparatus of US Patent Laid-Open No. 2013/0169710 may maintain a pressure applied to ink around each ejection opening within a certain range while circulating ink inside the liquid ejection head using a differential pressure generated between the ink supply path and the ink collection path.